The present invention relates to a device for tensioning a surgical appliance and relates particularly to such a device for tensioning compression plates used in the treatment of bone fractures.
Known for the tensioning of surgical compression plates is a plate tensioning device provided with a perforated strip element or strap, through which a cortical screw is screwable into one of two parts of a broken bone which have to be pressed together. This tensioning device is provided with a hook for hooking into the compression plate attached to the respective other part of the broken bone and with a tensioning screw to draw the hook towards the strap.
The mode of construction of this known tensioning device is very simple: A carrier, in which a screw thread is cut with an axis parallel to the strap, is connected fast with the strap and arranged to protrude at right angles from it. Engaging this thread is a tensioning screw which is so arranged that its head is on the side of the carrier remote from the strap. Mounted between the screw head and the carrier is a slide, which is secured against rotation by two pins, which are displaceably guided in bores of the carrier. This slide is provided with a draw hook for tightening the compression plate. This construction displays different disadvantages: Due to the fact that the slide is connected to the screw head at one place and engages at the compression plate at another plate, tilting forces arise, which can cause the slide to become wedged fast, so that the surgeon cannot ascertain on tightening of the tensioning screw whether the force exerted by him serves to overcome the friction forces provided by the wedging action or to exert compression on the separate parts of the fractured bone. He lacks the necessary information on the compressive force acting on the fracture location. A further disadvantage is that the hook, which is connected fast with the slide after the fastening of the strap of the tensioning device by means of the cortical screw, may be displaced only in the direction of the tensioning screw. Thus, the hook can no longer be displaced in a direction perpendicular to the screw. A third disadvantage is that with the tensioning screw screwed in, the cortical screw is not accessible, so that during the screwing-on of the strap and during the unscrewing, and also during any adjustment such as loosening the tensioning device which may become necessary, the tensioning screw with its free end remote from the head must not then project out of the threaded bore.
It is an object of the present invention to provide a tensioning device for a surgical appliance in which some at least of the aforementioned disadvantages are substantially reduced.